An arrangement in which, in an engine equipped with two intake ports corresponding to each cylinder, the intake ports being formed from straight ports, a swirl is generated by individually curving throat portions of the two intake ports is known from Patent Publication 1 below.
That is, a swirl is generated in a clockwise direction within the cylinder by making one intake port disposed on the right-hand side relative to the cylinder axis curve leftward so as to be connected to the inner periphery of the cylinder in a tangential direction, and another swirl is generated in a clockwise direction within the cylinder by making the other intake port disposed on the left-hand side relative to the cylinder axis first curve leftward so as to avoid the one intake port and then curve rightward in front of the one intake port so as to be connected to the inner periphery of the cylinder in a tangential direction.
Patent Publication 1: Japanese Patent Application Laid-open No. 7-34884